This invention relates to an improved process for pyrolyzing or retorting solid carbonaceous materials. More particularly, this invention relates to an improved process for recovering liquid hydrocarbons from such solid carbonaceous materials.
As is well known, shale oil is not a naturally occurring product, but rather is formed by the pyrolysis, retorting or distillation of organic material, commonly called kerogen, found in certain shale-like rock. As is also well known, the kerogen has limited solubility in ordinary solvents and, therefore, cannot be recovered by extraction. Upon strong heating, however, the kerogen decomposes into gaseous and liquid products which can then be separated from the remainder of the shale-like rock. In general, the remainder of the shale-like rock will contain residual carbonaceous material, which may be burned to supply heat to the pyrolysis step, and various inorganic constituents which may impact upon the pyrolysis in varying degrees if recycled to the pyrolysis step.
Heretofore, several processes have been proposed wherein the heat required to effect the pyrolysis, retorting or distillation is supplied by introducing externally heated solids into the retorting apparatus. A particularly preferred solid material is spent shale, i.e., the remainder of the shale-like rock after the kerogen has been converted and separated, which has been burned to produce solid particles having a temperature within the range from about 50.degree. to about 400.degree. F. above the desired pyrolyzing, retorting or distillation temperature. These solids are then combined with the shale-like rock feed to the pyrolyzer, retort or distillation apparatus at a ratio within the range from about 0.5:1 to about 20:1.
As indicated in U.S. Pat. No. 4,459,201, processes wherein spent shale is combusted and recycled to the retort as a source of heat are known to exhibit disadvantages such as reduced yield of liquid product as a result of the adsorption of liquid by the recycled solids. These type processes are also known to result in large amounts of fines in the liquid product, apparently as a result of the poor particle integrity of the recycled solids. Moreover, it has been discovered that such processes exhibit a reduced yield of liquid product also as a result of conversion of the liquid to gases. This reduction in the yield of liquid product appears to be even more costly than that caused by adsorption of liquid product. The need, then, for an improved process wherein combusted, spent carbonaceous material can be used as a source of heat without a reduction in the yield of liquid product and an increase in the fines content in the liquid product is believed to be readily apparent.